.TH std::throw_with_nested 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::throw_with_nested \- std::throw_with_nested

.SH Synopsis
   Defined in header <exception>
   template< class T >                            \fI(since C++11)\fP
   [[noreturn]] void throw_with_nested( T&& t );

   If std::decay<T>::type is a non-final non-union class type that is neither
   std::nested_exception nor derived from std::nested_exception, throws an exception of
   an unspecified type that is publicly derived from both std::nested_exception and
   from std::decay<T>::type, and constructed from std::forward<T>(t). The default
   constructor of the nested_exception base class calls std::current_exception,
   capturing the currently handled exception object, if any, in a std::exception_ptr.

   Otherwise, throws std::forward<T>(t).

   Requires that std::decay<T>::type is CopyConstructible.

.SH Parameters

   t - the exception object to throw

.SH Return value

   \fI(none)\fP

.SH Example



   Demonstrates construction and recursion through a nested exception object.


// Run this code

 #include <exception>
 #include <fstream>
 #include <iostream>
 #include <stdexcept>
 #include <string>

 // prints the explanatory string of an exception. If the exception is nested,
 // recurses to print the explanatory of the exception it holds
 void print_exception(const std::exception& e, int level =  0)
 {
     std::cerr << std::string(level, ' ') << "exception: " << e.what() << '\\n';
     try
     {
         std::rethrow_if_nested(e);
     }
     catch (const std::exception& nestedException)
     {
         print_exception(nestedException, level + 1);
     }
     catch (...) {}
 }

 // sample function that catches an exception and wraps it in a nested exception
 void open_file(const std::string& s)
 {
     try
     {
         std::ifstream file(s);
         file.exceptions(std::ios_base::failbit);
     }
     catch (...)
     {
         std::throw_with_nested(std::runtime_error("Couldn't open " + s));
     }
 }

 // sample function that catches an exception and wraps it in a nested exception
 void run()
 {
     try
     {
         open_file("nonexistent.file");
     }
     catch (...)
     {
         std::throw_with_nested(std::runtime_error("run() failed"));
     }
 }

 // runs the sample function above and prints the caught exception
 int main()
 {
     try
     {
         run();
     }
     catch (const std::exception& e)
     {
         print_exception(e);
     }
 }

.SH Possible output:

 exception: run() failed
  exception: Couldn't open nonexistent.file
   exception: basic_ios::clear

.SH See also

   nested_exception  a mixin type to capture and store current exceptions
   \fI(C++11)\fP           \fI(class)\fP
   rethrow_if_nested throws the exception from a std::nested_exception
   \fI(C++11)\fP           \fI(function template)\fP
